The present invention relates to a heat shield for a casting furnace, such as a furnace for casting superalloy parts having oriented structures. The heat shield is disposed between a heating zone of the furnace and a cooling zone in which the molten metal is solidified.
It is known to utilize furnaces for casting metal wherein a mold is placed within the furnace and molten metal is poured into the mold. After a specified heating time at specific temperatures, the mold is then moved from the heating zone of the furnace into a zone wherein the metal within the mold is cooled and solidified. The precise heating temperatures in conjunction with heating rates and cooling rates enable the casting of a metal, such as a superalloy, having a specific oriented metallic structure.
French Pat. No. A 2,604,378 describes a heat shield in conjunction with such a furnace wherein the heat shield is mounted between the heating and cooling zones of the furnace to prevent the heat exchange therebetween. The heat shield in this invention performs the heat insulation function, but at the same time allows the mold to pass between the heating zone and the cooling zone.
U.S. Pat. No. 3,714,977 to Terkelsen illustrates a casting furnace having a heat shield wherein a mold is moved between a heating zone and a cooling zone. The heat shield in Terkelsen is attached to the mold mounting device such that it surrounds the mold. As the mold moves downwardly, the heat shield bears against a stationary structure and stops while the movement of the mold continues into the cooling zone.
The known devices do not provide adequate heat insulation between the heating and cooling zones in those instances wherein the geometry of mold is complex. Consequently, drops in the thermal gradient take place which causes variations, particular increases, in the sizes of the primary dendrites of the cast parts. Such increased size dendrites substantially degrade the mechanical properties of the cast parts and require a more complex subsequent heat treatment.